Cisco CCNP Security Core (SCOR) 350-701Visibility and EnforcementMedium
A security engineer is configuring QoS policies on a Cisco router to prioritize voice and video traffic while ensuring that critical business applications receive sufficient bandwidth, even during periods of network congestion. Which QoS mechanism should be applied to classify and mark packets at the network edge to enable downstream devices to apply appropriate prioritization?
- ATraffic policing
- BCongestion management
- CClassification and marking
- DTraffic shaping
Show answer & explanationAnswer & explanation
Correct answer: C. Classification and marking
Classification and marking is the foundational QoS mechanism for identifying specific traffic types (like voice/video) and then tagging them (e.g., with DSCP values) so that downstream QoS mechanisms (like queuing or shaping) can apply appropriate prioritization or treatment.
Why the other options are wrong
- A. Traffic policing limits bandwidth but doesn't primarily classify or mark for prioritization; it drops excess traffic.
- B. Congestion management refers to queuing mechanisms that handle traffic when links are congested but requires packets to be classified and marked first.
- D. Traffic shaping buffers and smooths out traffic bursts, but relies on prior classification and marking to know which traffic to shape.
QoS Classification and Marking
The initial steps in a Quality of Service (QoS) policy where incoming network traffic is identified (classified) based on various criteria (e.g., source/destination IP, port, application) and then assigned a specific priority or class of service (marked) using fields like DSCP or CoS.
- Classification identifies traffic types.
- Marking tags packets for prioritization by downstream devices.
- Common marking fields: DSCP (IP Layer 3) and CoS (Ethernet Layer 2).
- Typically performed at the network edge (ingress) to ensure end-to-end QoS.
Memory trick: First, identify and tag your traffic; then, manage the flow.